I have a cube build underway and was wondering on the sump design. Its a 60cm cube sump and was wondering about the need for three compartments. I wont be doing a dsb, so is there any need for a middle compartment? I will have a skimmer and NP reactor

ok
Leave the RO chamber. And put one divider at about 70-30 of the sump. That would give you big enough area for skimmer and reactor. Plus return chamber of 30% should be big enough to handle the fluctuation when the ATU decides not to work. Plus you would have enough space next to the return pump to place another pump to feed that frag tank....

ok
Leave the RO chamber. And put one divider at about 70-30 of the sump. That would give you big enough area for skimmer and reactor. Plus return chamber of 30% should be big enough to handle the fluctuation when the ATU decides not to work. Plus you would have enought space necxt to the return pump to place another pump to feed that frag tank....

ok
Leave the RO chamber. And put one divider at about 70-30 of the sump. That would give you big enough area for skimmer and reactor. Plus return chamber of 30% should be big enough to handle the fluctuation when the ATU decides not to work. Plus you would have enough space next to the return pump to place another pump to feed that frag tank....

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Agreed here, if you do not have a separate chamber for the return pump the water level might fluctuate too much for the skimmer.